Check out past exams first to get some idea of topics- this is always your go-to when you want an idea of topics in this subject. Focus your notes and discussion on Australian values and what features of Australian English (e.g. idioms, slang, swearing, diminutives) shows these values- e.g. laidback culture due to convict past and distinct identity from Brits. Remember that Australian identity is diverse- so don't forget about ethnolects (special focus on Aboriginal English) and variation in Australian English based on socioeconomic background, gender, location (this is also where your 3 accents come in) etc and how these groups use language to establish their own unique take on Australian culture and create an Australian identity that may differ from the mainstream. Have some examples of all these ready to go, post them in the threads!
convictcreations.com is a fabulous resource to read up on Australian culture. Many essay prompts will be something along the lines of "how does Australian English show our values" or it will pick a specific Australian cultural value and ask you to explain how that specific Australian value is displayed through Australian English, others will talk about the changing face of Australian English and Americanisation- e.g. e-communication is making things more global and younger people may say "dude" instead of "mate". Other prompts may ask you to talk about an ethnolect of your choice.
I personally find that some students focus too much on the little history lesson and how our culture and values came to be, this can be used to support your points but I wouldn't linger on it. Enjoy your opportunity to openly swear on essays

Hope that helped
